Power Flow Analysis And Software Development Of Medium And Low Voltage DC Distribution Network

With the development of distributed generation and DC loads,a safe,reliable,and efficient DC distribution network will become an important direction for the development of future distribution networks.The DC distribution network based on the voltage source converter has the advantages of strong controllability,less power quality problems,and good economy.However,the access of a large number of power electronic equipment also introduces a power flow calculation problem that is different from that of the AC distribution network.The current DC power flow calculation method cannot meet the requirements of multi-voltage DC power flow calculation with more flexible control methods,more diverse operating modes,and richer load types.Therefore,it is necessary to study the power flow analysis method suitable for the future development direction of DC distribution network.This paper studies the power flow calculation method of DC distribution system based on voltage source converter.The specific work content is as follows:(1)The main equipment model of the multi-voltage DC distribution system is studied,and the power flow calculation model considering the converter loss is established,and the loss expression method and the calculation method of loss parameters are given.Then a power flow model of the DC/DC converter considering the loss is established.The control methods of voltage source converter and DC/DC converter and their equivalent methods in power flow calculation are analyzed in detail.(2)The influence of voltage source converter and DC/DC converter control strategies on power flow calculations is analyzed.According to different control strategies,different power flow solving methods are given,and several effective solutions are given when the network power flow exceeds the limit.Taking the improved IEEE 33 bus DC distribution network model as an example,the simulation results verify the effectiveness and feasibility of the proposed loss model and power flow solution method.(3)The models of voltage source converter converter and DC/DC converter in power flow calculation under true bipolar and pseudo bipolar are established.Based on the established DC power flow model,it focuses on the analysis of the method of constructing power flow equations for different types of DC loads in true bipolar and pseudo bipolar networks.Different power flow calculation models are given for constant power,constant current,and constant resistance loads.Furthermore,the steps and methods for solving the network power flow equations are given.Finally,taking the national key research and development plan-Suzhou Demonstration Project as an example,the simulation verifies the effectiveness of the power flow model of the multi-voltage DC distribution network under different wiring modes.(4)Based on theoretical analysis,the development and design of the evaluation software for the DC power distribution system was completed,and the code development of the power flow calculation module based on the C++compilation environment was realized on the Visual Studio 2019 platform,and the software test was successfully passed.